1. Field of the Invention
The present invention relates generally to antenna devices, and more particularly to an antenna device having an element pattern and a microstrip line extending from the feeding point of the element pattern formed on one side (surface) of a dielectric substrate, and having a ground pattern opposing the microstrip line formed on the other side (surface) of the dielectric substrate.
2. Description of the Related Art
In these years, a radio communications technology using UWB (Ultra Wideband), which enables radar positioning and communications at high data transfer rate, has attracted attention. Since 2002, USB has been approved for use in a frequency band of 3.1 to 10.6 GHz by the U.S. FCC (Federal Communications Commission).
UWB is a communication method that communicates pulse signals in an ultra wideband. Accordingly, antennas used for UWB are required to have a configuration that enables transmission and reception in an ultra wideband.
As an antenna for use in at least the FCC-approved 3.1-10.6 GHz band, an antenna having a conic or teardrop-shaped feeding body disposed on a flat ground plate has been proposed (Taniguchi, T. and Takehiko Kobayashi (Tokyo Denki University); “An Omnidirectional and Low-VSWR Antenna for the FCC-approved UWB Frequency Band,” Institute of Electronics, Information, and Communications Engineers, B-1-133, B201, Mar. 22, 2003).
However, since the conventional antenna device having a conic or teardrop-shaped feeding body disposed on a flat ground plate is large in size, there has been a demand for reduction in the size and thickness of the conventional antenna device.
Accordingly, there is proposed a technique that reduces the size and thickness of this type of antenna device by forming an element pattern and a ground pattern of conductive patterns on a dielectric substrate.
FIGS. 1A and 1B are diagrams showing a conventional antenna device 10.
The conventional antenna device 10 includes a dielectric substrate 11, an element pattern 12, a microstrip line 13, and a ground pattern 14.
The dielectric substrate 11 is formed of, for example, an FR-4 substrate having a length L31 of substantially 40 mm and a width W31 of substantially 30 mm. The element pattern 12 and the microstrip line 13 are formed on one side (surface) of the dielectric substrate 11, and the ground pattern 14 is formed on the other side (surface) of the dielectric substrate 11.
The element pattern 12 is shaped like a home plate and has a length L41 of substantially 15 mm and a width W41 of substantially 16 mm. The microstrip line 13 extends from a feeding point Ps of the element pattern 12.
The ground pattern 14 is formed on the X2 side of the feeding point Ps of the element pattern 12 on the other side (surface) of the dielectric substrate 11. The ground pattern 14 has a length L42 of substantially 25 mm and a width of substantially 30 mm, which is the same as the width W31 of the dielectric substrate 11.
Regarding loop antennas used for communications in low-frequency bands, an antenna device having an element formed with a conductive pattern on a flexible substrate has been proposed. (See, for example, Japanese Laid-Open Patent Application No. 2000-196327.)
In view of mounting these types of ultra-wide frequency band antenna devices in various communications devices, there is a strong demand for reduction in their sizes without degradation of characteristics such as VSWR.